The present invention relates to nonvolatile memory devices and programming methods.
Nonvolatile memory devices retain stored data in the absence of applied power. Among the broader class of nonvolatile memory devices, flash memory has been widely adopted for use within contemporary electronics such as computers, memory cards, portable music systems, cell phones, etc.
Flash memory may be divided into two general classes: NOR type and NAND type in accordance with its constituent interconnection logic between memory cells and bit lines. NOR flash memory provides relatively high data access speed, but is less susceptible to integration and consumes more power during operation. In contrast, NAND flash memory is relatively slower, but enjoys much higher integration density and reduced current consumption.
In conventional NAND flash memory, a single word line is shared by a plurality of so-called “program cells” (i.e., memory cells to be programmed) and program-inhibited cells (i.e., memory cells inhibited for programming). Program operations for NAND flash memory typically employed certain self-boosting schemes to prevent the program-inhibited cells from being inadvertently programmed during the programming operation.